Security Bootcamp 2013 - Mitigate DDoS attack with effective cost - Nguyễn Chấn Việt

Mitigate DDoS attackwith effective cost

Nguyễn Chấn Việt

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The Growth of DDoS Attacks

• Malware• Exploit

10/29/2013 11:16 AM www.securitybootcamp.vn

Classification• Volume Based Attacks –The attacker tries to saturate the bandwidth of the target’s

website by flooding it with a huge quantity of data. This category includes ICMP floods,UDP floods and other spoofed-packet floods. The magnitude of Volume Based Attacksis measured in bits per second (Bps).

• Protocol Attacks –The attacker’s goal is to saturate the target’s server resources orthose of intermediate communication equipment (e.g., Load balancers) by exploitingnetwork protocol flaws. This category includes SYN floods, Ping of Death, fragmentedpacket attacks, Smurf DDoS and more. The magnitude of Protocol Attacks ismeasured in Packets per second.

• Application Layer (Layer 7) Attacks – Designed to exhaust the resource limits of Webservices, application layer attacks target specific web applications, flooding them witha huge quantity of HTTP requests that saturate a target’s resources. Examples ofapplication layer DDoS attacks include Slowloris, as well as DDoS attacks that targetApache, Windows, or OpenBSD vulnerabilities. The magnitude of application layerattacks is measured in Requests per second.


What we care ?• Exhausting resources like:

– CPU– Memory/Buffers– I/O operations– Disk space– Network bandwidth


Where to start ?• Go through all devices on network, from

L2 switches to backend servers andidentify possible leaks, bottlenecks,attack vectors, applicable DoS attacks,vulnerabilities ... and mitigate or(rate)limit them


Infrastructure• Hosting and VM is not good idea


[1]


Architecture• Rule: Defence in depth (multi-layer)


OS Tuning• *nix is good choice

• Rule : If not used, turn off


/etc/sysctl.conf tuning• net.netfilter.nf_conntrack_tcp_timeout_syn_recv = 2

net.ipv4.tcp_syn_retries = 3net.ipv4.tcp_synack_retries = 1net.ipv4.tcp_syncookies = 1net.ipv4.tcp_max_syn_backlog = 8192net.ipv4.tcp_mem = 786432 1048576 1572864net.ipv4.tcp_rmem = 4096 87380 1048576net.ipv4.tcp_wmem = 4096 16384 1048576net.ipv4.tcp_max_orphans = 2048


Layer 3-4• Stateful Firewall

– Iptables– Tuning connections tracking

• Rule : Deny all, allow selective


Layer 7• WAF : to filter what firewall missed at IP

layer– Mod_security

• Why not snort ?


Layer 7• Choosing webserver

– Nginx is the best• Tuning webserver

– Improve Apache with mod_reqtimeout• Caching is very important

– Static cache– memcached


Patching• Keep Your System Up-to-date• Example :

– Slowloris : based on missing CRLF– Slow Read attack : based on TCP persist

timer exploit– Apache Range Header attack


Proactive with NSM• Logs is very important• My suggestion : Syslog-ng + Splunk


Proactive with NSM


Proactive with NSM


Proactive with NSM• Alternative :


Logstash is a free tool formanaging events and logs. Ithas three primarycomponents, an Inputmodule for collecting logsfrom various sources

ElasticSearch is thisawesome distributable,RESTful, free Lucenepowered searchengine/server. UnlikeSOLR, ES is very simpleto use and maintain andsimilar to SOLR, indexingis near realtime.

Kibana is a presentation layerthat sits on top of Elasticsearch toanalyze and make sense of logsthat logstash throws into Elasticsearch; Kibana is a highlyscalable interface for Logstashand ElasticSearch that allows youto efficiently search, graph,analyze and otherwise makesense of a mountain of logs.

Proactive with NSM


[2] Case Study


Our suggestion• Diagram


Our suggestion• Router with high throughput

• reverse proxy servers :– 32Gb RAM, 10Gb NIC, Quad Core I7, SSD

disk (for internal I/O better)– Linux OS, running IPTables + apache

(worker MPM) + mod_security


Our suggestion• cache servers :

– Using SSD Disk– Application cache (ex : xcache/APC for

PHP, …)– Generic cache : Apache Traffic Server


Cloud-based Solutions• For large DDoS attack (e.g Spamhaus

was DDoS by 300Gb/s of traffic), weneed a third-party :– Incapsula– CloudFlare


Cloud-based Solutions


Simple but effective• If you can determine C&C servers, just

null route them


Testing• Test your network and devices by

simulating real DoS attack (LOIC/HOIC,hping, slowhttptest, thc-ssl-dos, pktgen,... )


Conclusion• This approach is not “silver bullet” for

preventing DDoS attacks• There isn’t “a technique” for mitigrating

DDoS– DDoS Mitigation = Hardened System +

Money


Thank you !


Technology

Security Bootcamp 2013 - Mitigate DDoS attack with effective cost - Nguyễn Chấn Việt